On 11.08.22 15:59, Peter Xu wrote: > On Thu, Aug 11, 2022 at 12:34:35PM +0200, David Hildenbrand wrote: >> Reason is that uffd-wp doesn't clear the uffd-wp PTE bit when >> unregistering and consequently keeps the PTE writeprotected. Reason for >> this is to avoid the additional overhead when unregistering. Note >> that this is the case also for !hugetlb and that we will end up with >> writable PTEs that still have the uffd-wp PTE bit set once we return >> from hugetlb_wp(). I'm not touching the uffd-wp PTE bit for now, because it >> seems to be a generic thing -- wp_page_reuse() also doesn't clear it. > > This may justify that lazy reset of ptes may not really be a good idea, > including anonymous. I'm indeed not aware of any app that do frequent > reg/unreg at least. Yeah. QEMU snapshots come to mind, but I guess the reg/unreg overhead is the smallest issue. > > I'll prepare a patch to change it from uffd side too. > > Thanks again for finding this problem. YW! -- Thanks, David / dhildenb
